High temperature heating unit and method of making same



R. REICHMANN HIGH TEMPERATURE HEATING UNIT AND METHOD 0E MAKING SAMEApril 28, 1942.

Filed April 50, 1940 WITNESSES:

Patented Apr. 28, 1942 HIGH TEDIPERATURE HEATING UNIT AND METHOD 0FMAKING SAME Reinhold Reichmann, Berlin, Germany, assignor toWestinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., acorporation of Pennsylvania Application April 30, 1940, Serial No.332,508 In Germany February 10, 1939 4 Claims.

This invention relates, generally, to electric heating units of theresistor type, and more specically relates'to such units built for hightemperature operation even in an oxidizing atmosphere. v

A heating unit, in accordance with my invention, comprises, as theresistance element, a suitably-formed wire or rod of a highly refractorymetal, such as, for example, tungsten, molybdenum, and their alloys, andother similar metals capable of attaining very high temperatures withoutmelting; the wires being, preferably, wound around a ceramic refractorycarrier or support which has grooves in its outer portions in which thewire disposed. To protect the wire from harmful infliuences,particularly from oxidation while in e highly heated condition, theheating wire or conductor as aforesaid, located in the cuter groove ofthe carrier but to fully embed it, I close the groove by an additionalceramic layer, preferably hinting the groove, and fused to the main bodyof the carrier after the wire has been placed inthe groove. The heaterof my invention is completed by placing the aforesaid structure within asnugly-fitting ceramic tube, but, in some instances, coating thecompleted inner wire carrier with a gas-tight glaze or enamel beforelnserting it into the tube. It is an object of my invention to providea` high temperatures, such as, for example, temperatures of 1400* C. andabove, in which the heating unit has a comparatively long, useful lifeand may be made of highly refractory metals, such as, for example,tungsten, molybdenum, their alloys, or other highly refractory materialshaving similar properties but which, at high temgroove or indentation 3in the outer portion of the carrier I, the lateral boundaries of thegroove extending beyond the wire 2 by a small amount.

' The groove 2 Ais preferably a helix running along peratures, areextraordinarily senstitive to oxidation. The subject matter of myinvention is schematically shown in the drawing in which Fig. 1comprises a fragmentary cross sectional view longitudinally of the unitwith'parts broken away and parts shown in elevation for clarity ofillustration; and Fig. 2 is a, fragmentary sectional view of. amodification.

In accordance with the general principles of obtains. The manner inwhich the unit described may be produced is subject to variations, thus,for example, it is preferred to use a substance for the closure i whichis the same as that of the heating carrier l. This substance may be ofwell known high temperature insulating refractories, such assillimanlte, sintered emery, mullite, or other similar refractorlesgenerally comprising silicates or oxides of metals. The groove may beclosed by first forming a plastic `thread of the ceramic material andthen winding it over the tops of the groove. The thread may be given aform when it is produced which is particularly suitable for its functionfor closing the groove.

In the drawing, two forms of threads are shown. Thus the closure I'ls a,thread which fits across the top edges of the groove, while the closure4 is a thread which has a thickened portion which protrudes slightlyinto the groove 3 with the lateral projections, of the protrudingportion abutting the sides of the groove, and the main body .lying onthe surface of the carrier i. 'Ihe thread for closing the groove may besecured to the carrier byring after it is put on, or by heating of theresistance wire itself to the necessary temperatures for fusing theplastic mass. Preferably, it is desirable to cover the outer surface ofthe resulting unit with a thin glaze or enamel to further render it gasimpervious.

In accordance with the teachings of my copending application Serial No.273,891, flied May 16, 1939, the groove in the carrier should bedimensioned in such manner that its cross sectional area is somewhatlarger than that of the heating wire disposed in it, but should not bemore than 20% greater, and preferably less, and suitable terminals maybe provided. The aforesaid application has. since the filing of the invstant application, matured into Patent No. 2,208,-

342, granted July 16, 1940.

I claim as my invention:

1. A heatingunit comprising a tubular ceramic.

member having an outer convoluted groove, a non-metallic refractoryclosure for said groove, shaped to substantially match the top ol' saidgroove, a high-temperature refractory metal in said groove having anoriginal cross-sectional area which is less than that of said groovewhen closed by said closure, said refractory metal being of the typewhich'swells through heat-treatment at high temperatures to ll saidgroove as closed by said closure.

2. A high-temperature heating unit comprising, a tubular ceramic body ofcylindrical form,

a helical groove on the outside of said body, a helical non-metallicrefractory closure closing said groove, said closure substantiallymatching said groove, a high-temperature metallic refractory heatingelement swelled in said groove through heating at high temperatures, anda. snug-fitting gas-tight non-metallic refractory outer cover aroundsaid body and closure.

3. A high-temperature heating unit comprising, a tubular ceramic bodyof'cylindrical form,

I a helical groove on the outside of said body, a

temperature metallic refractory resistor material of the type which hasan increased cross-sectional area, after suitable heat-treatment; themethod which comprises disposing said resistor material in said groove,closing said groove with a ceramic closure in such a. manner that thecross-sectional area of said groove is larger than that of said resistormaterial therein, and heating said member, resistor material andclosure, to gas-tightly fuse said closure to said member and to swellsaid resistor material in said groove, glazing the resulting structure,and then fitting a gas-tight, non-metallic refractory cover over it.REINHOLD REICHMANN.

